This invention relates generally to propellers, vanes, impellers, and paddles of the type typically employed on aircraft, ships, wind-powered electric generators, windmills, turbine engines, etc. More particularly, the present invention is directed to a mechanism for automatically changing the pitch of blades utilized in such propellers and similar types of devices.
It is generally advantageous to provide the capability of varying the pitch or angle of attack of aircraft propeller blades, for example, in order to accommodate different flight conditions. Propellers whose pitch angle may be varied in flight are known as constant speed propellers. Various mechanisms are known for varying the pitch angles of propellers and other types of blades while they are rotating about a central shaft. Most of these mechanisms are a maze of gears and governors electrically or hydraulically actuated and represent effective, but expensive, ways in which pilots may regulate the pitch of propellers during flight.
U.S. Pat. No. 1,482,690 to Lanzius is directed to a propeller in which an axially movable collar causes each blade shank to rotate as it engages a slot in the shank. Centrifugal weights are located at 90 degrees to the propeller blades. The propeller blades do not extend or retract due to centrifugal force, and their rotation is fixed by a helical groove in the propeller shaft.
U.S. Pat. No. 4,374,631 to Barnes is directed to a windmill speed limiting system in which only the blade tips, rather than the entire blade, are adapted to extend during operation. As the blade tips extend, their pitch angle changes in accordance with a slotted cam in a bushing.
U.S. Pat. No. 2,126,202 to McColly is directed to a governor for windmills that utilizes a helix in a slide guide to allow the windmill blade to change pitch to limit the windmill RPM.
U.S. Pat. No. 2,510,216 to Figley is directed to an apparatus for controlling the pitch angle of aircraft propellers manually from the cockpit by means of a cable and pulley arrangement. The cable and pulley regulate radial movement of an extendable shaft within a hollow propeller. A pin following a helical groove in the extendable shaft varies the pitch of the propeller as the pilot operates the cable and pulley derangement.
U.S. Pat. No. 4,439,108 to Will is directed to a windmill in which centrifugal force is used to feather the rotors to control rotor speed. The windmill rotors do no extend or retract, but are mounted at a predetermined compound angle to the hub and are not in direct alignment with the center of the hub. As wind speed increase, the offset arrangement of the rotors and centrifugal force causes a reduction in the pitch angle of the rotors to thereby produce a braking effect.
U.S. Pat. No. 4,365,937 to Hiebert, deceased et al. is directed to an adjustable pitch propeller drive in which pitch changes are effected by a rack and pinion arrangement controlled by a hydraulic cylinder.
U.S. Pat. No. 2,415,421 to De Filippis is directed to an adjustable propeller that employs a helical cut-out or slot in a hollow stem of each blade and a camming pin in engagement with the helical slot to impart radial motion to the blades, as well as corresponding pitch angle changes.
U.S. Pat. No. 1,953,682 to Kelm is directed to an automatic variable pitch propeller in which a shifting pin follows a helical or cam slot in a guide tube to effect pitch changes corresponding to radial motion of the propeller blades caused by centrifugal force developed by the rotating propeller.
U.S. Pat. No. 2,282,077 to Moore is directed to variable pitch propeller in which blade turning pins or studs seated in the propeller shanks follow arcuate cam slots in hub sleeves to effect pitch changes corresponding to radial motion of the propeller blades caused by centrifugal force developed by the rotating propeller.
U.S. Pat. No. 2,264,568 to Hamilton is directed to mechanism for automatically feathering the blades of a model airplane propeller when the engine stops. A cross pin follows spiral slots in a bushing to effect pitch changes corresponding to radial motion of the propeller blades caused by centrifugal force developed by the rotating propeller.
U.S. Pat. No. 2,457,576 to Littrell is directed to a variable pitch propeller that is controlled manually from the cockpit by means of an electric motor controlling a ring gear turning a pinion to move a nut inwardly or outwardly in a spiral groove.
U.S. Pat. Nos. 2,108,245 and 2,120,168 to Ash, Jr. are directed to helicopter rotors employing telescoping airfoil sections controlled from the cockpit by means of coil springs and wound cables.
U.S. Pat. No. 2,005,343 to Kent is directed to a variable propeller in which set screws project through a hub block into communication with each end of an arcuate slot to thereby adjustably limit the range of pitch variation of the propeller.
Those of the above prior art references that describe systems for automatically varying the pitch of propeller blades by centrifugal force that is developed by the rotating propeller all employ elements containing either a slot or a groove that is strictly linear, arcuate or helical in shape. This results in a linear relationship between propeller speed and propeller pitch, which is undesirable from an operational standpoint.
It would be advantageous to provide different rates of change of propeller pitch as a function of propeller speed or RPM to accommodate different ground or flight operations. For example, over a range of propeller speeds at which taxi operations may occur, it may be desirable to maintain the same or nearly the same propeller pitch. It may then be desirable to provide a greater rate of change of propeller pitch when increasing the propeller speed to a range suitable for flight climb conditions and to maintain a particular propeller pitch nearly constant over the range of propeller speeds suitable for cruise conditions.
It is therefore the principal object of the present invention to provide an automatic centrifugal force variable pitch propeller in which the relationship between propeller speed and propeller pitch is nonlinear; that is, the rate of change of propeller pitch is not constant with changes in propeller speed.
It is another object of the present invention to provide an automatic variable pitch propeller in which the individual propeller blades are mechanically linked to insure that inward and outward travel of the blades is in concert.
These and other objects are accomplished in accordance with one illustrated embodiment of the present invention by providing at least a pair of propeller blades mounted within a housing, each of the propeller blades being arranged for inward and outward axial travel and simultaneous incremental rotation about its longitudinal axis, a pair of mirror image cam/guide plates fixedly mounted within the housing adjacent a shaft end of each of the propeller blades, each of the mirror image cam/guide plates having a nonlinear, discontinuous configuration, and a pin follower transversely extending from the shaft end of each of the propeller blades and being positioned for engagement with the nonlinear, discontinuous configuration in each of the mirror image cam/guide plates, whereby an increase in the speed at which the propeller blades turn produces an increase in centrifugal force causing outward travel of the propeller blades and incremental rotation of each of the blades about its longitudinal axis corresponding to movement of each of the pin followers in the associated pair of mirror image cam/guide plates. In another illustrated embodiment of the present invention, a slotted cylinder fixedly positioned over the shaft end of each of the propeller blades is employed in place of the mirror image cam/guide plates.